The present invention generally relates to brake systems and more particularly relates to an operating unit for an electrohydraulic braking system of the xe2x80x98brake-by-wirexe2x80x99 type.
An operating unit of this general type is disclosed in DE 198 22 411 A1. The characteristic feature of the prior-art operating unit involves that the simulator element is formed of a metal pleated bellows that accommodates the simulator spring without preload. The above-mentioned third valve device which is arranged in the connection between the interior of the pleated bellows and the supply chamber of the second pressure chamber is comprised of a seat valve that is mechanically operable by the movement of the second piston by means of a two-arm tilting lever mounted on an axis of rotation. The prior-art operating unit especially suffers from the disadvantage of the complicated design of the actuation of the third valve device causing considerable costs of manufacture and assembly. The bleeding of the interior of the pleated bellows is also considered as a problem.
In view of the above, an object of the present invention is to disclose an operating unit of the above-mentioned type that permits being manufactured at low costs and allows easy bleeding.
According to the present invention, this object is achieved in that the simulator element is formed of a (simulator) piston that can be acted upon by the pressure introduced in the first pressure chamber, and in that the third valve device is formed of a seal arranged at the second piston and by the mouth area of a channel provided in the range of movement of the seal and constituting the second hydraulic connection. These provisions allow deactivating the simulator effect within the emergency operation, where minimum possible lost travels are realized until the first pressure buildup in the vehicle wheel brakes.
A second solution of the present invention to the object to be achieved includes that in an operating unit where a second hydraulic connection between the simulator chamber and the pressure fluid supply reservoir is obviated, the simulator element is formed of a hydraulic simulator piston, and that the third valve device is formed of a seal arranged at the second piston and by the mouth area of a channel provided in the range of movement of the seal, the said channel constituting the hydraulic connection and being connected to the first pressure chamber, on the one hand, and to a hydraulic chamber separated from the simulator chamber by the simulator piston, on the other hand.
In another favorable embodiment of the second solution, a second hydraulic connection may be provided between the simulator chamber and the pressure fluid supply reservoir.
Another favorable aspect of the present invention arranges for hydraulic resistors or throttling means, respectively, in the hydraulic connection or in the second hydraulic connection. The mentioned provisions achieve an effective damping during actuation of the simulator.
In a third and a fourth solution to the above-mentioned object, the simulator element is formed of a hydraulic simulator piston in operating units wherein the third valve device closes or opens the first or the second hydraulic connection and is configured as a seat valve and includes a valve member that is biased in its closing direction by a spring, and the third valve device is operable by means of a transverse member axially abutting on the second piston. The above-mentioned fourth solution is especially appropriate for an actuating unit where there is no second hydraulic connection between the simulator chamber and the pressure fluid supply reservoir.
Favorable aspects of the present invention can be taken from sub claims 11 to 16.
It is considered advantageous to use a travel sensor signal for detecting the driver""s request. The travel sensor signal is output by a travel measuring system integrated in the housing in another embodiment of the subject matter of this invention, wherein the first piston is configured as a component of the measuring system that senses the actuating travel.
In a travel measuring system that functions very reliably, signal generator elements of the travel measuring system are mounted on the cylindrical surface of the first piston, and the signal pickups of the system are arranged in the housing.